Semiconductor device and fabrication method thereof

ABSTRACT

A method for fabricating semiconductor device is disclosed. A substrate having a first transistor on a first region, a second transistor on a second region, a trench isolation region, a resistor-forming region is provided. A first ILD layer covers the first region, the second region, and the resistor-forming region. A resistor material layer and a capping layer are formed over the first region, the second region, and the resistor-forming region. The capping layer and the resistor material layer are patterned to form a first hard mask pattern above the first and second regions and a second hard mask pattern above the resistor-forming region. The resistor material layer is isotropically etched. A second ILD layer is formed over the substrate. The second ILD layer and the first ILD layer are patterned with a mask and the first hard mask pattern to form a contact opening.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. application Ser. No. 15/402,245 filed on Jan. 10, 2017, entitled “SEMICONDUCTOR DEVICE AND FABRICATION METHOD THEREOF”, and the entire content of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates generally to a method for fabricating a semiconductor device. More particularly, the present invention relates to a method of integrating thin film resistor processes to fabricate low-resistance local interconnect contact.

2. Description of the Prior Art

As semiconductor integrated circuit technology continues to improve, semiconductor chips have smaller and more complex circuit designs. At the same time, the number and density of functional devices in each chip region is increasing due to innovation requirements.

A standard semiconductor chip includes a plurality of semiconductor electronic components, such as transistors interconnected by an interconnection scheme to form a complete functional circuit. Since the dimensions of the above-mentioned semiconductor electronic components have become smaller in recent years, the contact holes may not align with the underneath conductive area such as the gate or the source/drain regions, resulting in increased contact resistance thereby affecting device performance.

SUMMARY OF THE INVENTION

According to one embodiment, the present invention provides a method for fabricating a semiconductor device. First, a substrate having a first transistor in a first region, a second transistor in a second region, a trench isolation region isolating the first region from the second region, a resistor-forming region, and a first interlayer dielectric (ILD) layer over the first region, the second region, and the resistor-forming region is provided. The first transistor comprises a first terminal selected from the group consisting of a first gate and a first source/drain region, and the second transistor comprises a second terminal selected from the group consisting of a second gate and a second source/drain region. Next, a resistor material layer and a capping layer are formed over the first region, the second region, and the resistor-forming region. The capping layer and the resistor material layer are patterned to form a first hard mask pattern above the first region and the second region, and forma second hard mask pattern above the resistor-forming region. Next, isotropic etching is performed on the resistor material layer. A second interlayer dielectric (ILD) layer is deposited over the substrate. Finally, the second ILD layer and the first ILD layer are patterned with a mask and the first hard mask pattern to form a contact opening. The contact opening exposes the first terminal, the second terminal, and the trench isolation region.

According to another embodiment, a method for fabricating a semiconductor device is provided. First, a substrate having a first transistor in a first region, a second transistor in a second region, a trench isolation region isolating the first region from the second region, a resistor-forming region, and a first interlayer dielectric (ILD) layer over the first region, the second region, and the resistor-forming region is provided. The first transistor comprises a first terminal selected from the group consisting of a first gate and a first source/drain region, and the second transistor comprises a second terminal selected from the group consisting of a second gate and a second source/drain region. Next, a resistor material layer and a capping layer are formed over the first region, the second region, and the resistor-forming region. The capping layer and the resistor material layer are patterned to form a hard mask pattern above the trench isolation region and a thin film resistor above the resistor-forming region. Next, a second interlayer dielectric (ILD) layer is deposited on the hard mask pattern and the thin film resistor. The second ILD layer and the first ILD layer are patterned with a mask and the hard mask pattern to form a first contact opening and a second contact opening. The first contact opening exposes the first source/drain region, and the second contact opening exposes the second source/drain region.

According to another embodiment, the present invention provides a semiconductor device, including: a substrate having a first transistor in a first region, a second transistor in a second region, a trench isolation region isolating the first region from the second region, and a resistor-forming region, wherein the first transistor includes a first terminal selected from the group consisting of a first gate and a first source/drain region, and the second transistor includes a second terminal selected from the group consisting of a second gate and a second source/drain region; a first interlayer dielectric (ILD) layer over the first region, the second region, and the resistor-forming region; a thin film resistor over the resistor-forming region, the thin film resistor including a resistor material layer and a capping layer on the resistor material layer; a hard mask pattern over the first region and the second region, the hard mask layer including the resistor material layer; a second interlayer dielectric (ILD) layer covering the hard mask pattern, the thin film resistor, and the first ILD layer; a contact opening penetrating through the second ILD layer, the capping layer, the resistor material layer, and the first ILD layer to expose the first terminal and/or the second terminal; and a local interconnect contact disposed in the contact opening.

These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 to FIG. 8 are schematic, cross-sectional diagrams showing an exemplary method of fabricating a semiconductor transistor device in accordance with one embodiment of the invention.

FIG. 9 to FIG. 18 are schematic, cross-sectional diagrams showing an exemplary method of fabricating a semiconductor transistor device in accordance with another embodiment of the invention.

DETAILED DESCRIPTION

In the following detailed description of the invention, reference is made to the accompanying drawings, which form a part hereof, and in which is shown, by way of illustration, specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments may be utilized and structural, logical and electrical changes may be made without departing from the scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims, along with the full scope of equivalents to which such claims are entitled.

Before describing the preferred embodiment, the following description will be given for specific terms used throughout the specification.

The term “etch” or “etching” is used herein to generally describe a fabrication process of patterning a material, such that at least a portion of the material remains after the etch is completed. For example, it should be understood that the process of etching silicon involves the steps of patterning a photoresist layer above the silicon with an exposure and development technique, and then removing the areas of silicon no longer protected by the photoresist layer. As such, the areas of silicon protected by the photoresist layer will remain behind after the etch process is complete. In another example, however, etching may also refer to a process that does not use a photoresist layer, but still leaves behind at least a portion of the material after the etching process is completed.

The above description serves to distinguish the term “etching” from “removing.” When etching a material, at least a portion of the material remains behind after the process is completed. In contrast, when removing a material, substantially all of the material is removed in the process. In some embodiments, “removing” is considered to be a broad term that may incorporate etching. The term “patterning” typically includes lithography and etching processes.

The term “substrate,” “semiconductor substrate” or “wafer” as described throughout, is most commonly a silicon substrate or a silicon wafer. The term “substrate” or “wafer” may also, however, refer to any semiconductor material such as germanium, gallium arsenide, indium phosphide, and the like.

FIG. 1 to FIG. 8 are schematic, cross-sectional diagrams showing an exemplary method of fabricating a semiconductor transistor device in accordance with one embodiment of the invention. First, as shown in FIG. 1, a substrate 10 is provided, such as silicon substrate. According to the embodiment of the invention, the substrate 10 includes a plurality of active regions AA₁ to AA₄ and a resistor-forming region RA. A plurality of trench isolation regions TI₁ to TI₃ for isolating the plurality of active regions AA₁ to AA₄ are formed on the main surface 10 a of the substrate 10, in which the trench isolation region TI₁ is provided between the active region AA₁ and the active region AA₂, the region TI₂ is provided between the active region AA₃ and the active region AA₄, and the resistor-forming region RA is provided directly above the trench isolation region TI₃.

According to the embodiment of the invention, a transistor T₁ is provided in the active region AA₁, a transistor T₂ is provided in the active region AA₂, a transistor T₃ is provided in the active region AA₃, and a transistor T₄ is provided in the active region AA₄. In addition, a passing gate PG is provided on the trench isolation region TI₂.

According to the embodiment of the invention, the transistor T₁ includes a gate structure MG₁ and a source/drain region SD₁, the transistor T₂ includes a gate structure MG₂ and a source/drain region SD₂, the transistor T₃ includes a gate structure MG₃ and a source/drain region SD₃, and the transistor T₄ includes a gate structure MG₄ and a source/drain region SD₄. According to an embodiment of the present invention, an epitaxial layer such as SiP epitaxial layer, SiC epitaxial layer or SiGe epitaxial layer may be provided in each of the source/drain regions SD₁ to SD₄. According to an embodiment of the present invention, a silicide layer may be provided in each of the source/drain regions SD₁ to SD₄.

According to an embodiment of the present invention, a sacrificial layer (not shown) may be selectively formed on each of the gate structures MG₁ to MG₄, but is not limited thereto. The spacers may be formed on the side walls of the gate structures MG₁ to MG₄. According to an embodiment of the present invention, the transistors T₁ to T₄ may be fin field effect transistors (FinFETs). The gate structures MG₁ to MG₄ may be formed by a replacement metal gate (RMG) process, but is not limited thereto.

According to an embodiment of the present invention, a first interlayer dielectric layer 12 is formed on the substrate 10 and covers the plurality of active regions AA₁ to AA₄ and the resistor-forming region RA. According to an embodiment of the present invention, the first interlayer dielectric layer 12 may include silicon oxide or a low dielectric constant material, but is not limited thereto.

FIG. 1 shows the structure of the first interlayer dielectric layer 12 after the planarization process, wherein the planarization process may be a chemical mechanical polishing process. According to an embodiment of the present invention, the first interlayer dielectric layer 12 is flush with the top surfaces of the gate structures MG₁ to MG₄.

Next, as shown in FIG. 2, a dielectric buffer layer 22 is deposited, in a blanket manner, on the first interlayer dielectric layer 12. The dielectric buffer layer 22 is in direct contact with the first interlayer dielectric layer 12 and the exposed top surfaces of the gate structures MG₁ to MG₄. Next, a resistor material layer 24 is deposited, in a blanket manner, over the dielectric buffer layer 22, and a capping layer 26 is deposited, in a blanket manner, over the resistor material layer 24. According to the embodiment of the invention, the dielectric buffer layer 22 may include silicon oxide, etc. The resistive material layer 24 may include titanium nitride, tantalum nitride, chromium silicide, or nickel-chromium alloys, etc. The capping layer 26 may include silicon nitride, but is not limited thereto.

As shown in FIG. 3, a photolithography and etching process are performed to pattern the capping layer 26 and resistor material layer 24, thereby forming a hard mask pattern HM₁, a hard mask pattern HM₂, a hard mask pattern HM₃, and a hard mask pattern HM₄ above, respectively, the active region AA₁, the active region AA₂, the active region AA₃, and the resistor-forming region RA. According to the embodiment of the present invention, each of the hard mask patterns HM₁ to HM₄ includes a portion of the capping layer 26 and a portion of the resistor material layer 24. According to the embodiment of the present invention, the above-mentioned etching process may include an anisotropic dry etching process.

As shown in FIG. 4, an isotropic etching process such as a wet etching process is performed to isotropically etch the resistor material layer 24 of the hard mask patterns HM₁ to HM₄, so that the resistor material layer 24 of each of the hard mask patterns HM1 to HM4 are retracted inward to form respective undercut structures C₁ to C₄. According to the embodiment of the present invention, a thin film resistor TR is formed on the first interlayer dielectric layer 12 after completion of the isotropic etching process.

Next, as shown in FIG. 5, a second interlayer dielectric (ILD) layer 14 is deposited over the substrate 10. According to the embodiment of the present invention, the second interlayer dielectric layer 14 may include silicon oxide or a low dielectric constant material, but is not limited thereto. According to the embodiment of the present invention, the second interlayer dielectric layer 14 covers the capping layer 26 of each of the hard mask patterns HM₁ to HM₄, is in direct contact with and covers the dielectric buffer layer 22, and deposits into the undercut structures C₁ to C₄ of the hard mask patterns HM₁ to HM₄. According to the embodiment of the present invention, the second interlayer dielectric layer 14 is not indirect contact with the first interlayer dielectric layer 12.

Next, as shown in FIG. 6, a photoresist pattern 30 having an opening 30 a and an opening 30 b is formed on the second interlayer dielectric layer 14. The opening 30 a is located between the active region AA₁ and the active region AA₂ and overlaps with the trench isolation region TI₁. According to the embodiment of the present invention, the opening 30 a may partially overlap with the active area AA₁ and the active area AA₂. The opening 30 b is located between the active region AA₃ and the trench isolation region TI₂ and partially overlaps with the active region AA₃ and the trench isolation region TI₂.

An anisotropic dry etching process is performed by using the photoresist pattern 30 and the hard mask patterns HM₁ to HM₃ together as an etching resist mask to etch down the second interlayer dielectric layer 14, dielectric buffer layer 22 and the first interlayer dielectric layer 12 through the opening 30 a and the opening 30 b, thereby forming a contact opening 40 a and a contact opening 40 b. The contact opening 40 a exposes the source/drain region SD₁ of the transistor T₁, the source/drain region SD₂ of the transistor T₂, and the trench isolation region TI₁ between the source/drain region SD₁ and the source/drain region SD₂. The contact opening 40 b exposes the source/drain region SD₃ of the transistor T₃ and the trench isolation region TI₂. Subsequently, the photoresist layer 30 is removed.

As shown in FIG. 7, a photoresist pattern 50 having an opening 50 a and an opening 50 b is then formed on the substrate 10, wherein the opening 50 a is located directly above the passing gate PG, and the opening 50 b is located directly above the thin film resistor TR. Then, an anisotropic dry etching process is performed to etch down the second interlayer dielectric layer 14, the dielectric buffer layer 22 and the portion of the gate through the opening 50 a, thereby forming a contact opening 40 c that can communicate with the contact opening 40 b. At the same time, the second interlayer dielectric layer 14 and the hard mask pattern HM₄ are etched down through the opening 50 b to form a resistor contact opening 40 d that exposes a terminal of the thin film resistor TR. According to the embodiment of the invention, the resistor contact opening 40 d does not penetrate through the resistor material layer 24. Subsequently, the photoresist pattern 50 is removed.

As shown in FIG. 8, a conductive material layer 60, such as titanium nitride or tungsten, is deposited into the resistor contact opening 40 d and the contact openings 40 a, 40 b and 40 c. Next, a chemical mechanical polishing (CMP) process is performed to remove the conductive material layer 60 outside the resistor contact opening 40 d and the contact openings 40 a, 40 b and 40 c, thereby forming a resistor contact 60 c in the resistor contact opening 40 d, a local interconnect contact 60 a in the contact opening 40 a, and a local interconnect contact 60 b in the contact openings 40 b and 40 c.

FIG. 9 to FIG. 15 are schematic, cross-sectional diagrams showing an exemplary method of fabricating a semiconductor transistor device in accordance with another embodiment of the invention. First, as shown in FIG. 9, a substrate 10 is provided, such as silicon substrate. According to the embodiment of the invention, the substrate 10 includes a plurality of active regions AA₁ to AA₄ and a resistor-forming region RA. A plurality of trench isolation regions TI₁ to TI₃ for isolating a plurality of active regions AA₁ to AA₄ are formed on the main surface 10 a of the substrate 10, in which the trench isolation region TI₁ is provided between the active region AA₁ and the active region AA₂, The region TI₂ is provided between the active region AA₃ and the active region AA₄, and the resistor-forming region RA is provided directly above the trench isolation region TI₃.

According to the embodiment of the invention, a transistor T₁ is provided in the active region AA₁, a transistor T₂ is provided in the active region AA₂, a transistor T₃ is provided in the active region AA₃, and a transistor T₄ is provided in the active region AA₄. In addition, a passing gate PG is provided on the trench isolation region TI₂.

According to the embodiment of the invention, the transistor T₁ includes a gate structure MG₁ and a source/drain region SD₁, the transistor T₂ includes a gate structure MG₂ and a source/drain region SD₂, the transistor T₃ includes a gate structure MG₃ and a source/drain region SD₃, and the transistor T₄ includes a gate structure MG₄ and a source/drain region SD₄. According to an embodiment of the present invention, an epitaxial layer such as an SiP epitaxial layer, SiC epitaxial layer or SiGe epitaxial layer may be provided in each of the source/drain regions SD₁ to SD₄. According to an embodiment of the present invention, a silicide layer may be provided in each of the source/drain regions SD₁ to SD₄.

According to an embodiment of the present invention, a sacrificial layer (not shown) may be selectively formed on each of the gate structures MG₁ to MG₄, but is not limited thereto. The spacers may be formed on the side walls of the gate structures MG₁ to MG₄. According to an embodiment of the present invention, the transistors T₁ to T₄ may be fin field effect transistors (FinFETs). The gate structures MG₁ to MG₄ may be formed by a replacement metal gate (RMG) process, but the process is not limited thereto.

According to an embodiment of the present invention, a first interlayer dielectric layer 12 is formed on the substrate 10 and covers the plurality of active regions AA₁ to AA₄ and the resistor-forming region RA. According to an embodiment of the present invention, the first interlayer dielectric layer 12 may include silicon oxide or a low dielectric constant material, but is not limited thereto.

FIG. 9 shows the structure of the first interlayer dielectric layer 12 after the planarization process, wherein the planarization process may be a chemical mechanical polishing process. According to an embodiment of the present invention, the first interlayer dielectric layer 12 is flush with the top surfaces of the gate structures MG₁ to MG₄.

Next, as shown in FIG. 10, a dielectric buffer layer 22 is deposited, in a blanket manner, on the first interlayer dielectric layer 12. The dielectric buffer layer 22 is in direct contact with the first interlayer dielectric layer 12 and the top surfaces of the exposed gate structures MG₁ to MG₄. A resistor material layer 24 is deposited, in a blanket manner, over the dielectric buffer layer 22, and a capping layer 26 is deposited, in a blanket manner, over the resistor material layer 24. According to the embodiment of the invention, the dielectric buffer layer 22 may include silicon oxide, etc. The resistive material layer 24 may include titanium nitride, tantalum nitride, chromium silicide, or nickel-chromium alloys, etc. The capping layer 26 may include silicon nitride, but is not limited thereto.

As shown in FIG. 11, a photolithography and etching process are performed to pattern the capping layer 26 and resistor material layer 24, thereby forming a hard mask pattern HM₁ above the trench isolation region TI₁, a hard mask pattern HM₂ above the trench isolation region TI₂ and the active region AA₄, and a thin film resistor TR above the resistor-forming region RA. According to the embodiment of the present invention, each of the hard mask patterns HM₁ to HM₂ includes a portion of the capping layer 26 and a portion of the resistor material layer 24. According to the embodiment of the present invention, the above-mentioned etching process may include an anisotropic dry etching process.

Next, as shown in FIG. 12, a second interlayer dielectric (ILD) layer 14 is deposited over the substrate 10. According to the embodiment of the present invention, the second interlayer dielectric layer 14 may include silicon oxide or a low dielectric constant material, but is not limited thereto. According to the embodiment of the present invention, the second interlayer dielectric layer 14 covers each of the hard mask patterns HM₁ to HM₂, is in direct contact with and covers the dielectric buffer layer 22, and covers the thin film resistor TR. According to the embodiment of the present invention, the second interlayer dielectric layer 14 is not in direct contact with the first interlayer dielectric layer 12.

Next, as shown in FIG. 13, a photoresist pattern 70 having openings 70 a to 70 d is formed on the second interlayer dielectric layer 14, wherein the opening 70 a is aligned with the source/drain region SD₁ of the transistor T₁, the opening 70 b is aligned with the source/drain region SD₂ of the transistor T₂, the opening 70 c is aligned with the source/drain region SD₃ of the transistor T₃, and the opening 70 d is aligned with the source/drain region SD₄ of the transistor T₄.

An anisotropic dry etching process is performed by using the photoresist pattern 70 and the hard mask patterns HM₁ to HM₂ together as an etching resist mask to etch down the second interlayer dielectric layer 14, dielectric buffer layer 22 and the first interlayer dielectric layer 12 through the openings 70 a to 70 d, thereby forming contact openings 80 a to 80 d. The contact opening 80 a exposes the source/drain region SD₁ of the transistor T₁, the contact opening 80 b exposes the source/drain region SD₂ of the transistor T₂, the contact opening 80 c exposes the source/drain region SD of the transistor T₃, and the contact opening 80 d exposes the source/drain region SD₄ of the transistor T₄. Subsequently, the photoresist layer 70 is removed.

As shown in FIG. 14, a photoresist pattern 90 having openings 90 a to 90 c is then formed on the substrate 10. The opening 90 a is located directly above the hard mask pattern HM₁ and the trench isolation region TI₁, the opening 90 b is located directly above the hard mask pattern HM₂, and the opening 90 c is located directly above the thin film resistor TR. Then, an anisotropic dry etching process is performed to etch down the second interlayer dielectric layer 14 and the capping layer 26 through the openings 90 a to 90 c, thereby forming a connecting opening 80 e that can communicate with the contact openings 80 a and 80 b, forming a connecting opening 80 f that can communicate with the contact openings 80 c and 80 d, and forming a resistor contact opening 80 g. The resistor contact opening 80 g exposes a terminal of the thin film resistor TR. According to the embodiment of the invention, the connecting opening 80 e exposes the resistor material layer 24 of the hard mask pattern HM₁ and the connecting opening 80 f exposes the resistor material layer 24 of the hard mask pattern HM₂.

According to the embodiment of the present invention, the resistor contact opening 80 g may be formed by using another photo mask and a separate etching step. The resistor contact opening 80 g does not penetrate through the resistor material layer 24. Subsequently, the photoresist pattern 90 is removed.

As shown in FIG. 15, a conductive material layer 100, such as titanium nitride or tungsten, is deposited into the resistor contact opening 80 g, the contact openings 80 a to 80 d, and the connecting openings 80 e and 80 f. Next, a chemical mechanical polishing (CMP) process is performed to remove the conductive material layer 100 from the top surface of the second interlayer dielectric layer 14, thereby forming a resistor contact 100 c in the resistor contact opening 80 g, a local interconnect contact 100 a in the contact openings 80 a and 80 b and the connecting opening 80 e, and a local interconnect contact 100 b in the contact openings 80 c and 80 d and the connecting opening 80 f. According to the embodiment of the present invention, the local interconnect contact 100 a is in direct contact with the resistor material layer 24 of the hard mask pattern HM₁, and the local interconnect contact 100 b is in direct contact with the resistor material layer 24 of the hard mask pattern HM₂.

According to the embodiment of the present invention, the local interconnect contact 100 a traverses the trench isolation region TI₁ and is in direct contact with the resistor material layer 24 of the hard mask pattern HM₁. The local interconnect contact 100 b traverses the trench isolation region TI₂ and is in direct contact with the resistor material layer 24 of the hard mask pattern HM₂.

FIG. 16 is a schematic showing a layout of a two-input NOR gate circuit, wherein the local interconnect contact 100 b in FIG. 15 is applied. FIG. 17 is a schematic diagram showing a cross-section along the tangent I-I′ in FIG. 16.

As shown in FIG. 16, the two-input NOR gate circuit includes a plurality of gates WL₁ to WL₄ which are interleaved with the fin structures F₁ to F₄ to form a plurality of transistors such as NMOS transistors N_(a) and N_(b) and PMOS transistors P_(a) and P_(b). The corresponding signals can be provided through the metal layer patterns 201 to 205. For example, the signal at the input point a is coupled to the gate WL₃ through the metal layer pattern 202, and the signal at the input point b is coupled to the gate WL₂ through the metal layer pattern 203, and signal V_(DD) is coupled to a terminal of the PMOS transistor P_(b) through the metal layer pattern 201 and a contact structure 301, and signal V_(ss) is coupled to a terminal shared by the NMOS transistors N_(a) and N_(b) through the metal layer pattern 204 and a contact structure 302, and the Z output point is coupled to a terminal of the NMOS transistor N_(b) through the metal layer pattern 205 and the local interconnect contact 303.

As shown in FIG. 17, the local interconnect contact 303 traverses two gates WL₂ and WL₃, which is similar to the local interconnect contact 100 b in FIG. 15, and the local interconnect contact 303 is in direct contact with the resistor material layer 24 traversing two gates WL₂ and WL₃. After the local interconnect contact 303 is completed, a dielectric layer 510 may be deposited, such as nitrogen-doped carbide (NDC), and an intermetal dielectric layer 512. Then, a metal layer pattern 205 is formed in the intermetal dielectric layer 512 and the dielectric layer 510, for electrical connection to the local interconnect contact 303.

FIG. 18 is a schematic showing a layout diagram of a two-input NAND gate circuit in which the local interconnect contact 100 b in FIG. 15 is applied. The same regions and elements are represented by the same numerals.

As shown in FIG. 18, the two-input NAND gate circuit includes a plurality of gates WL₁ to WL₄ which are interleaved with the fin structures F₁ to F₄ to form a plurality of transistors such as NMOS transistors N_(a) and N_(b) and PMOS transistors P_(a) and P_(b). The corresponding signal can be provided through the metal layer patterns 201 to 205. For example, the signal at the input point a is coupled to the gate WL₃ through the metal layer pattern 202, and the signal at the input point b is coupled to the gate WL₂ through the metal layer pattern 203. Signal V_(DD) is coupled to a terminal shared by the PMOS transistors P_(a) and P_(b) through the metal layer pattern 201 and a contact structure 301, signal V_(ss) is coupled to a terminal of the NMOS transistor N_(b) through the metal layer pattern 204 and a contact structure 302, and the output point Z is coupled to a terminal of the PMOS transistor P_(a) and a terminal of the PMOS transistor P_(b) through the metal layer pattern 205 and the local interconnect contact 303.

Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims. 

What is claimed is:
 1. A semiconductor device, comprising: a substrate having a transistor, wherein the transistor comprises a gate and a source/drain region; a first interlayer dielectric layer beside the gate; a dielectric buffer layer directly on the gate and the first interlayer dielectric layer; a second interlayer dielectric layer above the dielectric buffer layer; a local interconnect directly contacting the source/drain region through the first interlayer dielectric layer, the dielectric buffer layer, and the second interlayer dielectric layer; and a material layer comprising titanium nitride, tantalum nitride, chromium silicide, or nickel-chromium alloys, and disposed directly on the dielectric buffer layer, wherein the material layer is next to the local interconnect and is isolated from the local interconnect.
 2. The semiconductor device according to claim 1, wherein the first interlayer dielectric layer comprises silicon oxide or a low dielectric constant material.
 3. The semiconductor device according to claim 1, wherein the first interlayer dielectric layer is flush with a top surface of the gate.
 4. The semiconductor device according to claim 1, wherein the dielectric buffer layer comprises silicon oxide.
 5. The semiconductor device according to claim 1 further comprising a trench isolation region under the local interconnect, wherein the local interconnect directly contacting the trench isolation region.
 6. The semiconductor device according to claim 1 further comprising a capping layer over the material layer.
 7. The semiconductor device according to claim 6, wherein the capping layer comprises silicon nitride.
 8. The semiconductor device according to claim 6, wherein the material layer is retracted inward to form an undercut structure. 